Sir, that is not because of your plugs either you're pushing it too far or your speedo is off
@CH_UMAIRCHEEMA Regarding the overheating, spark plugs are not making your car overheat, check elsewhere, this is not your problem..
Check the pipes, see if water body is working, if you have a thermostat valve, check if it opens at the correct temperature. Check if the fins of the radiator are clean to let the air flow through them.. check your car's timing, or your radiator might be clogged, get it serviced.. there shouldn't be any leaks..